Information bias of social gradients in sickness absence: a comparison of self-report data in the Norwegian Mother and Child Cohort Study (MoBa) and data in national registries

Table 1 Education level distribution and sickness absence risk in mid-pregnancy according to source of data: 49637 MoBa mothers

Source of data and education level	N	%	Sickness absence cases^a	Risk^a	95% CI
Register data			14,731	0.478	0.473 to 0.484
Education level (15 missing)
Lower secondary or less	2431	5	689	0.634	0.605 to 0.663
Upper secondary, basic	1638	3	559	0.630	0.598 to 0.661
Upper secondary, complete	11,484	23	3506	0.539	0.527 to 0.551
Tertiary, undergraduate	25,523	51	8024	0.484	0.476 to 0.492
Tertiary, graduate	8546	17	1953	0.339	0.327 to 0.352
Self-report data			11,279	0.307	0.303 to 0.312
Education level (4207 missing)
Lower secondary or less	835	2	149	0.336	0.292 to 0.380
Upper secondary, basic	2076	5	455	0.337	0.312 to 0.362
Upper secondary, complete	10,981	24	2758	0.340	0.330 to 0.351
Tertiary, undergraduate	19,779	44	5268	0.318	0.310 to 0.325
Tertiary, graduate	11,759	26	2649	0.260	0.251 to 0.268

CI confidence interval
^aCases and risks restricted to 30,814 participants with register data and 36,684 participants with self-report data on both education and sickness absence; see Fig. 1

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